1. Field of Invention
The present invention relates to semiconductor light emitting devices, and more particularly, to multiple light emitting devices mounted on a shared submount.
2. Discussion of Related Art
It is known to control light emitting diodes (LEDs) to, for example, generate various colors, control on/off timing, or control brightness levels. In devices, which include LEDs with the three primary colors—red (R), green (G), blue (B)—varying the current of the three LEDs enables the generation of almost any color in the visible spectrum. Therefore, they are prime candidates to be used in, for example, color displays. Furthermore, of particular interest are devices capable of generating white light (consisting of R, G, and B components) because of their potential for replacing conventional light sources, such as light bulbs.
Related progress includes the following works. Mueller et al in U.S. Pat. Nos. 6,016,038 and 6,150,774 disclose a pulse width modulated current control for an LED lighting assembly, where each current-controlled unit is uniquely addressable and capable of receiving illumination color information on a computer network. The LEDs are controlled by a microprocessor to alter the brightness or the color of the generated light, for example by using pulse width modulated signals. This LED assembly is therefore capable of providing complex, predesigned patterns of light. However, the LEDs are packaged individually, and the driving logic is positioned separately from the LEDs, resulting in spatially extensive structures.
Mizutani et al. in Japanese patent JP7235624 disclose an LED lamp, wherein a package is formed of transparent resin, and the electrodes of an inverted LED device are bonded directly on the conducting pathways, leading outside the package. However this approach relies on the creation of several individual wire bonds, and thus does not eliminate the number one source of failure of LED systems, the breakdown of the wire bonds.
Finally, Liu et al. in U.S. Pat. No. 5,886,401 disclose an LED interconnection package, wherein the LED is situated on a substantially transparent substrate, having a contact surface with contact pads; a polymer film overlying the contact surface and having via openings; a substantially transparent support surrounding the LED and the substrate; and metallization overlying the polymer film and extending through the via openings for interconnecting the contact pads. An array of the disclosed LEDs mounted on a shared submount is then described. However, a switch circuit for controlling the LEDs is positioned outside the LED package, once again resulting in spatially extensive structures.
There are areas where marked improvement is desired. A higher density LED architecture is desired for space considerations, such as in applications where LED devices are integrated with other circuit elements, for example, on circuit boards. Higher densities are also advantageous to construct high power applications. Higher densities allow the creation of smaller LED assemblies, which resemble more closely an ideal point source of light; thus, the secondary optics, manipulating the emitted light, are simpler and cheaper to produce.